An adjustable band or clamp or non-adjustable clamp is placed about the greater curvature of the stomach in a vertical orientation. The band or clamp completely compartmentalizes the stomach between a small vertical pouch and the fundus and body of the stomach. The fundus and body of the stomach are excluded from nutrients and are separated from a long narrow channel where the food travels. A small passage at the level of the antrum allows gastric juices to empty from the fundus and body of the stomach. The clamp may be applied during open surgery in laproscopic surgery or using a single port technique, or through any natural orifice in NOTES (Natural Orifice Transluminal Endoscopic surgery) or using a hybrid surgical technique.